Fusible link



0. ROBERTS.

FUSIBLE LINK. APPLICATION FILED-FEB. 3. 1920.

1,357,347, Patented Nov. 2, 1920.

UNITED STATES PATENT OFFICE.

ODIN ROBERTS, OF BOSTON, MASSACHUSETTS, ASSIGNOB, TO FIRE PROTECTION SECURITIES COMPANY, OF BOSTON, MASSAGHUSETTS, .EL CORPORATION OF MASSACHUSETTS.

resists LINK.

Specification of Letters Patent.

Patented Nov. 2,1920.

Application filed February 3, 1920. Serial No. 356,103.

To all whom it may concern e it known that I, ODIN Roennrs, a citizen of the United States, and resident of Boston, in the county of Suffolk and State of Massachusetts, have invented new and useful Improvements in Fusible Links, of which the following is a specification.

My invention relates to fusible links, such as are employed on automatic sprinklers to restrain a valve under normal conditions and release it by disintegration. of the link itself under the influence of abnormal heat, the link being composed of separable members, normally held in assemblage as an integer by means of a fusible solder.

The object of this invention is to provide such a link which, when its parts are assembled and joined, will sustain a large proportion of the stress to which it is subjected by the resistant close contact of portions of the hard metal members, relying on the fusible solder to sustain only so much stress as is required to hold the hard metal members in position to function as aforesaid. Further; the object is to confine the location of stress-resisting opposed hard metal surfaces to a single area, and to surround this completely with portions of the link plates between which the fusible solder lies when the link is assembled, so that the opposed hard-metal surfaces which are relied on to resist the stress on the link are effectually sealed and protected against corrosion or deterioration, even when they are not coated at all with a film of solder.

Wherever fusible solder lies as a film be tween hard metal surfaces which are constantly strained with a tendency to move over or away from each other, the solder, especially when warmed, tends to yield a little, allowing the hard metal link members to creep; if this occurs, the valve which should be held tightly closed, will leak. Hard metal portions in direct contact with each other, especially if they have surfaces which lie at an angle with the line of stress nearly equal to their frictional angle of repose, resist creeping tendencies quite effectively, and require only a relatively slight restraining force to hold them in position.

The improvements in fusible link, herein described, reconcile the conflicting requirements, and provide a two-part link winch possesses a maximum of integral strength In the drawings hereto annexed, which illustrate my invention,-

Figure 1 is a central longitudinal section of a link; and a Fig. 2 is an elevation of one of the plates of which the assembled link is composed.

F or facility in manufacture, the link plates are preferably identical in dimensions and design, and are adapted to fit together head to tail. 'Each plate is composed of a sheet of such metal as copper, and is provided near one end with a hole A. which is adapted to engagement with a sprinkler strut, in a well known manner. At the other end the plate is cut out as at B, so that when two such plates are juxtaposed the hole A in one registers with the notch B in the other.

The plate is further shaped between dies, which without rupturing the plate press out from its fiat body two projections, preferably of elongated pyramidal form, with their long axes lying across the plate. The surfaces of these projections should be as nearly plane as possible, and the dies so shaped that the convex surface of the proj ection P will fit closely into the concavity formed by the projection P without bringing the major fiat faces of the plates into contact, but on the contrary leaving a slight clearance. The projection P which is to be a convex engaging member is, in the form shown for illustration, similar in shape but slightly larger in dimension than the proj ection P.

When two such plates are laid face to face, with the larger projection P fitting into the concavity of a smaller projection P, the excess of size possessed by the projection P, P, as compared with projections P, P, makes it impossible to bring the fiat faces of the plates together, so that these are suitably spaced apart for the reception of the fusible material l Properly formed holding pincers may be employed to press the interengaging projections very tightly together during the soldering process, which may consist of dipping the juxtaposed plates first into melted solder and then into cold water; or of spreading solder on the flat faces, and heating the plates while holding them tightly together.

The designed relative proportions of the projections P and P are such that they provide reliable means for securing a uniform spacing of the flat surfaces .of opposed plates, and therefore a uniformly thick film of fusible material between them, provided the plates are truly flat, and are not flexed during the soldering.

If it be desired, small projections as T may be struck out from the plates, so as still further to insure their proper and uniform spacing; but this is not necessary and is not recommended, since if such projections be accidentally too prominent, they will tend to interfere with the desired hard-metal contact between the interfitting projections.

By the exercise of care in shaping the dies which are employed to form the projections P and P, and by pressing the proj ections tightly together while the soldering is being done, there is little likelihood of admitting any fusible material between the inclined and contacting surfaces of the projections. By having these projections formed as shown, the convex surfaces of projections P automatically guide themselves to a secure and uniformly contacting seat in the ooncavities of projections P; this because each projection has two surfaces inclined to each other and meeting at substantially a linear apex.

When the link thus formed is subjected to'stress, the hard metal contacts of inclined surfaces of the projections assume the function of sustaining the imposed stress; there is little or no fusible material between them to introduce an element of weakness and permit creeping. The fusible material F, uniformly distributed over the relatively large flat plate surfaces, is amply able to hold the plates in position, even though the fusible material be warmed. l/Vhen, however, the fusible material melts, the unstable relation of the plates permits instant disintegration of the link, the plates sliding diagonally apart. Owing to the absence of fusible material between the sliding inclined surfaces of the projections P and P there is no chance that an initial spurt of water from the released valve will chill any fusible material while it is still in position to reunite any parts of theplates.

The oppositely protruding pyramidal projections P and P on each link plate are juxtaposed, so that their sides which are parallel to and nearest to the transverse axis of the link lie in the same inclined planes, thus forming a single area near the center of surface of the link, where the hard metal inclined surfaces are directly and intimately opposed.

At the inclined surfaces which meet in the planes marked 0, the stress of use tends to separate the surfaces, whereas the same stress presses together the inner inclined surfaces which meet in the plane marked I. Any of the solder F which, during the manufacture of the link, intruded itself into the regions marked 0 will serve usefully in com tributing to the adherence of the plates to each other. The region marked 1, however, is protected by the pyramidal surfaces which surround it, and lie between it and the solder l3, which, before it can find its way into the region I, must flow between these surrounding surfaces. The capillary action, which may initiate such flow from the space between the flat surfaces of the plates into such regions as are marked 0, serves to resist flow from those regions; consequently the stress resisting surfaces in the region marked 1 will be free from intruded solder.

It is considered undesirable toleave any contacting portions of fusible-link plates exposed to corrosion of any kind which, after lapse of time, might so bind the plates together as to retard or possibly prevent release of the sprinkler valve in'case of fire.

Therefore, the practice has been, to coat allcontacting parts of the links with solder, so that thus tinned the copper or bronze members shall be protected against corrosion. Thus, for the sake of observing one salutary precaution, the. link plates have been rendered susceptible to creeping, due to slight softening of solder, or its capability of slow flow under strain, even when at normal temperatures.

- While the contacting hard metal surfaces which in the fusible link herein described may meet without any solder film intervening, as at the surfaces marked I in Fig. 1, those contacting areas are as securely protected against action of corroding gases or liquids as if they were actually coated with solder, since during assemblage of the linkmembers these contacting areas are completely surrounded by soldered areas and are thus sealed. Of course, if it be desired,

these surfaces I can be solder-coated, and the resulting film be pressed very thin, without involving much probability that the link members will creep under strain.

A method of manufacture, calculated to produce a fusible link of the character above described in which the stress-resisting hard metal contact-surfacesshall be free from intervening solder, and also carry no acid flux which might tend to produce corrosion and adhesive, is suggested, as follows: I

Coat the surfaces of the plates with acid flux without any special pains to avoid coating the inclined surfaces intended to make close contact with each other; then apply solder, leaving the said surfaces without solder. Then after this solder has hardened wash the plates in a neutralizing solution to exposed areas of hard-metal, and afterward wash the plates in clear water and dry them. The plates may then be assembled in pairs, the solder remelted and the edges of the plates coated with solder in the usual manner.

What I claim and desire to secure by Letters Patent is:

1. A fusible link comprising two structurally similar plates, each having two juxtaposed similarly shaped transversely elongated pyramidal projections struck out from its body without rupture, in opposite directions, the adjacent transverse sides of the two projections lying in the same plane, and so disposed as to resist stress tending to separate the plates when the link is in service, and fusible adhesive material between and joining the opposed faces of the plates.

2. A fusible link comprising two structurally similar plates, each having two juxtaposed similarly shaped transversely elongated pyramidal projections struck out from its body without rupture, in opposite directions, one of said projections being slightly larger than the other, the adjacent trans verse sides of the two projections lying in the same plane, and so disposed as to resist stress tending to separate the plates when the link is in service, the plates assembled with the convexities of their respective larger projections fitting into the concavities of their respective smaller projections, and the opposed fiat surfaces of the plates spaced apart, and fusible adhesive material between and joining the opposed faces of the plates.

Signed by me at Boston, Massachusetts, this 2d day of Februar 1920.

DIN ROBERTS. 

